1. Field of the Invention
The present invention relates to a pump for use with an aquarium filter, and more particularly, to a pump for use with an aquarium filter having a main filter and a secondary biological filter.
2. Description of the Related Art
Copending application Ser. No. 08/004,677, filed Jan. 14, 1993, now U.S. Pat. No. 5,419,831 which is incorporated herein by reference, discloses an aquarium filter system which employs mechanical filtration to remove detritus from aquarium water and biological filtration to remove toxic substances such as ammonia from the water. Biological filtration relies on the presence of aerobic bacteria to convert the toxic substances to nontoxic or less toxic substances. The aerobic bacteria require oxygen to grow. In order to enhance growth of the aerobic bacteria, the filter systems of this type employ a rotatably mounted biological filter element positioned in a stream of aquarium water. One embodiment of such a filter system is illustrated in FIG. 1. The stream of water is directed below the filter element's rotational axis. As the filter element rotates, portions of the filter element and, accordingly, the aerobic bacteria, are alternately exposed to the atmosphere for growth and to the aquarium water for filtration.
The biological filter element in the '667 filter system is in the form of a turbine. The turbine may include a number of sheets made of porous filter material on which the aerobic bacteria grows. The sheets also serve as paddles. In such a filter system, aquarium water is preferably pumped through a mechanical filter element, and then past the biological filter element and finally back into the aquarium. As the water passes the biological filter element, it impinges on the paddles, thereby causing the biological filter element to rotate and alternately expose the aerobic bacteria to the atmosphere and to the aquarium water.
Because the aerobic bacteria relies on the rotation of the biological filter element for oxygen, it is important that the rate of rotation does not slow to an unacceptable level. Optimal bacteria growth occurs at relatively low rotation speeds (for example, less than 20 RPM). However, at such low speeds, erratic rotation of the biological filter element may occur due to normal imbalances in the biological filter element and friction in the bearing. Although satisfactory growth is likely to occur even if the rotation is somewhat erratic, erratic rotation is often perceived by the user as a problem and it may also result in less than optimal bacteria growth.
One solution to this problem is to provide a spray bar above the biological filter element which directs water onto the filter element in such a manner as to cause the filter element to rotate in the same direction as that caused by the water flowing under the filter element. As such, sufficient rotation of the biological filter element may be ensured. A drawback of this solution is the expense associated with the additional pumping power which has usually been required to supply water to the spray bar.